Biosorption of uranium(VI) by free and entrapped Chlamydomonas reinhardtii: kinetic,equilibrium and thermodynamic studies

Biosorption of uranium from aqueous solution onto the free and entrapped algae, “Chlamydomonas reinhardtii” in carboxymethyl cellulose (CMC) beads was investigated in a batch system using bare CMC beads as a control system. CMC can be a potential natural biosorbent for radionuclide removal as it contains carboxyl groups. However, limited information is available with the biosorption of uranium by CMC, when adsorption isotherm, kinetics and thermodynamics parameters are concerned. The biosorbent preparations were characterized by swelling tests, FTIR, and surface area studies. The effects of pH, temperature, ionic strength, biosorbent dosage, and initial uranium concentrations on uranium biosorption were investigated. Freely suspended algae exhibited the highest uranium uptake capacity with an initial uranium ion concentration of 1,000 mg/L at pH of 4.5 and at 25 °C. The removal of U(VI) ion from the aqueous solution with all the tested biosorbents increased as the initial concentration of U(VI) ion increased in the medium. Maximum biosorption capacities for free algal cells, entrapped algal cells, and bare CMC beads were found to be 337.2, 196.8, and 153.4 mg U(VI)/g, respectively. The kinetic studies indicated that the biosorption of U(VI) ion was well described by the pseudo-second order kinetic model. The variations in enthalpy and entropy for the tested biosorbent were calculated from the experimental data. The algal cells entrapped beads were regenerated using 10 mM HNO₃, with up to 94 % recovery. Algal cells entrapped CMC beads is a low cost and a potential composite biosorbent with high biosorption capacity for the removal of U(VI) from waters.     

Adsorption of uranium from aqueous solution using HDTMA+-pillared bentonite: isotherm, kinetic and thermodynamic aspects

The ability of hexadecyltrimethylammonium cation pillared bentonite (HDTMA⁺-bentonite) has been explored for the removal and recovery of uranium from aqueous solutions. The adsorbent was characterized using small-angle X-ray diffraction, high resolution transmission electron microscopy, and Fourier transform infrared spectroscopy. The influences of different experimental parameters such as solution pH, initial uranium concentration, contact time, dosage and temperature on adsorption were investigated. The HDTMA⁺-bentonite exhibited the highest uranium sorption capacity at initial pH of 6.0 and at 80?min. Adsorption kinetics was better described by the pseudo-second-order model and adsorption process could be well defined by the Langmuir isotherm. The thermodynamic parameters, ??G° (308?K), ??H°, and ??S° were determined to be ?31.64, ?83.84?kJ/mol, and ?169.49?J/mol/K, respectively, which demonstrated the sorption process of HDTMA⁺-bentonite towards U(VI) was feasible, spontaneous, and exothermic in nature. The adsorption on HDTMA⁺-bentonite was more favor than Na-bentonite, in addition the saturated monolayer sorption capacity increased from 65.02 to 106.38?mg/g at 298?K after HDTMA⁺ pillaring. Complete removal (??100%) of U(VI) from 1.0?L simulated nuclear industry wastewater containing 10.0?mg U(VI) ions was possible with 1.5?g HDTMA⁺-bentonite.     

Efficient uranium(VI) biosorption on grapefruit peel: kinetic study and thermodynamic parameters

The uranium(VI) biosorption by grapefruit peel was studied from aqueous solutions. Batch experiments was conducted to evaluate the effect of contact time, initial uranium(VI) concentration, initial pH, adsorbent dose, salt concentration and temperature. The equilibrium process was well described by the Langmuir, Redlich–Peterson and Koble–Corrigan isotherm models, with maximum sorption capacity of 140.79 mg g⁻¹ at 298 K. The pseudo second order model and Elovish model adequately describe the kinetic data in comparison to the pseudo first order model and the process involving rate-controlling step is much complex involving both boundary layer and intra-particle diffusion processes. The effective diffusion parameter D _i and D _f values were estimated at different initial concentration and the average values were determined to be 1.167 × 10⁻⁷ and 4.078 × 10⁻⁸ cm² s⁻¹. Thermodynamic parameters showed that the biosorption of uranium(VI) onto grapefruit peel biomass was feasible, spontaneous and endothermic under studied conditions. The physical and chemical properties of the adsorbent were determined by SEM, TG-DSC, XRD and elemental analysis and the nature of biomass–uranium (VI) interactions was evaluated by FTIR analysis, which showed the participation of COOH, OH and NH₂ groups in the biosorption process. Adsorbents could be regenerated using 0.05 mol L⁻¹ HCl solution at least three cycles, with up to 80% recovery. Thus, the biomass used in this work proved to be effective materials for the treatment of uranium (VI) bearing aqueous solutions.     

Adsorption of U(VI) onto the carboxymethylated chitosan/Na-bentonite membranes: kinetic,isothermic and thermodynamic studies

The carboxymethylated chitosan (CMC)/Na-bentonite (Na-Bt) composite membranes were prepared and throughly characterized. The Na-Bt/CMC mass ratio was optimized, and CB10 (membrane with Na-Bt/CMC mass ratio of 10%) was selected as the best membrane for U(VI) sorption. XPS analysis indicates that the main mechanism for UO₂²⁺ sorption onto CB10 is through inner-surface complexation. The sorption kinetics followed pseudo-second order model, indicating the chemisorption as the rate-controlling step. The U(VI) sorption on CB10 is endothermic and spontaneous, with the maximum mono-layer adsorption capacity of 115.6 mg/g at pH 5.0 and 298 K. Finally, the U(VI)-loaded CB10 can consecutively desorbed and reused for several cycles.     

Biosorption of Cd(II), Cr(III), and Cr(VI) by saltbush (Atriplex canescens) biomass: thermodynamic and isotherm studies

The biosorption data of Cd(II), Cr(III), and Cr(VI) by saltbush leaves biomass were fit on the Freundlich and Langmuir adsorption isotherms at 297 K. The Cd(II) and Cr(III) solutions were adjusted to pH 5.0 and the Cr(VI) solution was adjusted to pH 2.0. The correlation coefficient values indicated that the data fit better the Freundlich model. The maximal capacities (K(F)) were found to be 5.79 x 10(-2), 3.25 x 10(-2), and 1.14 x 10(-2) mol/g for Cr(III), Cd(II), and Cr(VI), respectively. Similar results were obtained using the Langmuir and the Dubinin-Radushkevick equations. Thermodynamic parameters calculated from the Khan and Singh equation and from the q(e) vs C(e) plot show that the equilibrium constants for the biosorption of the metals follow the same order of the maximal capacities. The negative Gibbs free energy values obtained for Cd(II) and Cr(III) indicated that these ions were biosorbed spontaneously. The mean free energy values calculated from the Dubinin-Radushkevick equation (10.78, 9.45, and 9.05 for Cr(III), Cr(VI), and Cd(II), respectively) suggest that the binding of Cd(II), Cr(III), and Cr(VI) by saltbush leaves biomass occurs through an ionic exchange mechanism.     

Removal of uranium(VI) and thorium(IV) ions from aqueous solutions by functionalized silica: kinetic and thermodynamic studies

Adsorption behavior of uranyl and thorium ions from synthetic radioactive solutions onto functionalized silica as sorbent has been investigated. The effect of contact time, initial concentration of radioactive solutions, sorbent mass, pH value and temperature on the adsorption capacity of the sorbent was investigated. Negative values of Gibbs free energy of adsorption suggested the spontaneity of the adsorption process on both functionalized silica with –NH₂ groups and with –SH groups. Positive values obtained for ΔH° indicates that the adsorption is an endothermic process. The adsorption isotherms were better fitted by Freundlich model and the adsorption kinetic was well described by the pseudo-second order equation. Desorption studies indicated that the most favorable desorptive reagents for UO₂ ²⁺ is HNO₃ 1 M and for Th⁴⁺ is EDTA 1 M solutions.     

Synthesis, characterization, thermodynamic and kinetic investigations on uranium (VI) adsorption using organic-inorganic composites: Zirconyl-molybdopyrophosphate-tributyl phosphate

Zirconyl-molybdopyrophosphate-tributyl phosphate (ZMPP-TBP) was a novel organic-inorganic composite adsorbent prepared by co-precipitation method and used in the adsorption of uranium from aqueous solution in batch adsorption experiments. The as-obtained product was characterized using SEM, energy dispersive X-ray spectroscopy (EDX), XRD and BET-N₂ adsorption measurements. The study had been conducted to investigate the effects of solution pH, temperature, contact time, initial concentration and coexisting ions. A maximum removal of 99.31% was observed for an initial concentration 5 mg/L, at pH 6.0 and an adsorbent dose of 1.0 g/L. The isothermal data were fitted with both Langmuir and Freundlich equations, but the data fitted the former better than the latter. According to the evaluation using the Langmuir equation, the maximum adsorption capacity of uranium (VI) was 196.08 mg/g at 293 K and pH 6.0. The pseudo-first-order kinetic model and pseudo-second-order kinetic model were used to describe the kinetic data, and the pseudo-second-order kinetic model was better. The thermodynamic parameter ΔG was calculated, the negative ΔG values of uranium (VI) at different temperature showed that the adsorption process was spontaneous. The good reusability of ZMPP-TBP also indicated that the ZMPP-TBP was a very promising adsorbent for uranium adsorption from aqueous solution.     

Biosorption of radiostrontium by alginate beads: application of isotherm models and thermodynamic studies

Radioactive strontium is one of the major radioactive contaminant and its contamination is a very serious concern. Therefore, there is a need for economic, effective, non-toxic, readily available and abundant adsorbent or biosorbent to remove strontium from solutions. In this study, biosorption of ⁸⁵Sr as a surrogate for ⁹⁰Sr onto alginate beads was investigated in a batch system. Alginate beads were prepared from Na-alginate via cross-linking with divalent calcium ions according to the egg box model. The effect of several parameters such as pH, initial strontium concentration, contact time, dosage of alginate beads and temperature were investigated. In order to optimize the design of biosorption system for the removal of strontium, it is important to establish the most appropriate correlation for equilibrium curves. The experimental isotherm data were described by 6 different biosorption isotherm models, namely Langmuir, Freundlich, Dubinin–Radushkevich, Temkin, Flory–Huggins and Brunauer, Emmer and Teller, with constants obtained from linear and non-linear regression methods. The thermodynamic parameters (?H°, ?S° and ?G°) for strontium biosorption were also determined. The results indicate that these alginate beads have a good potential for the biosorption of strontium from solutions.     

Adsorption behavior of uranium on polyvinyl alcohol-g-amidoxime: Physicochemical properties, kinetic and thermodynamic aspects

Amidoxime-based adsorbents are widely studied as the main adsorbent in the recovery of uranium from seawater.However,the adsorption rate and loading capacity of such adsorbents should be further improved due to the economic viability consideration.In this paper,polyvinyl alcohol functionalized with amidoxime(PVA-g-AO)has been prepared as a new adsorbent for uranium(Ⅵ)adsorption from aqueous solution.The physicochemical properties of PVA-g-AO were investigated using infrared spectroscopy(IR),scanning electron microscope(SEM),X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).Results showed that the ligand monomers were successfully grafted onto the matrixes.The XRD and XPS analysis showed that uranium was adsorbed in metal ionic form rather than in crystal form.Uranyl(U(Ⅵ))adsorption properties onto PVA-g-AO were evaluated.The adsorption of U(Ⅵ)by PVA-g-AO was fast,with an equilibrium time of less than 50 min.Additionally the maximum adsorption capacity reached 42.84 mg/g at pH 4.0.     

Biosorption of uranium(VI) from aqueous solution by Citrus limon peels: kinetics,equlibrium and batch studies

Citrus limon peel (exocarp) was chemically treated and used for removal of U(VI) ions from aqueous solution in a batch system. Optimization of U(VI) sorption parameters, i.e. medium pH, adsorbent amount, contact time, initial U(VI) ions concentration and temperature on the removal performance of both native and modified peels was studied. Adsorption capacity of the modified peel was near up to 4 times higher than of unmodified. The correlation regression coefficients show that the adsorption process can be well-defined by Langmuir equation. Additionally, it conforms to the pseudo-second order kinetic and Weber–Morris diffussion models well.

     

Biosorption of beryllium from aqueous solutions onto modified chitosan resin: Equilibrium,kinetic and thermodynamic study

The goal of the present work is the recovery of beryllium ion from their solution by modified chitosan hydrogel. Chitosan was chemically cross-linked with glutaraldehyde to prevent its dissolution in aqueous acidic solutions. The obtained chitosan/glutaraldehyde adsorbent was reacted with chloroacetic acid to produce carboxymethyl chitosan (CMC), which was converted into sodium form by reaction with sodium hydroxide solution to increase its hydrophilic properties. The chemically synthesized chitosan adsorbent contains carboxylate group that expected to have a strong affinity to beryllium ions according to the hard-soft acid-base concept by Pearson because that beryllium ion is a hard acid and has smaller ionic radii. The synthesized adsorbent was characterized and its affinity towards beryllium ions was tested. The different experimental parameters including pH, beryllium concentration, agitation period and temperature were studied to optimize the biosorption process. The maximum biosorption values of beryllium species on the investigated biosorbent are 44.96 and 36.72?mg/g at pH 1 and 5, respectively. Kinetics and thermodynamic parameters of the biosorption process were evaluated from kinetic and biosorption experiments. The adsorbed beryllium species were eluted with a 3?M H₂SO₄ solution.     

Adsorption behavior of uranium(VI) and other ionic species on cross-linked chitosan resins modified with chelating moieties

Cross-linked chitosan resins with catechol (catechol-type chitosan, type 1 and type 2), iminodiacetic acid (IDA-type chitosan), iminodimetylphosphonic acid (IDP-type chitosan), phenylarsonic acid (phenylarsonic acid-type chitosan), or serine (serine-type chitosan) were prepared for the collection and concentration of uranium(VI). The adsorption behavior of U(VI) and other ionic species, such as metal ions and oxo-acid ions, on the cross-linked chitosan (base material) and chitosan resins modified with chelating moieties was examined using a column procedure. Especially, the catechol-type chitosan (type 2) adsorbed U(VI) at pH 2-7, and selectively collected U(VI) at acidic pH regions by forming a stable chelate with hydroxyl groups of catechol moiety introduced to the chitosan. Also, the adsorption properties of cationic and anionic species present in aquatic media were elucidated. The adsorption ability for U(VI) was in the order: catechol-type chitosan (type 2) > serine-type chitosan > phenylarsonic acid-type chitosan > the others. The catechol-type chitosan (type 2) was useful for the collection and concentration of uranium(VI).     

The removal of uranium(VI) from aqueous solutions onto activated carbon: kinetic and thermodynamic investigations

The adsorption of uranium(VI) from aqueous solutions onto activated carbon has been studied using a batch adsorber. The parameters that affect the uranium(VI) adsorption, such as contact time, solution pH, initial uranium(VI) concentration, and temperature, have been investigated and optimized conditions determined (contact time 240 min; pH 3.0+/-0.1; initial uranium concentration 100 mg/L; temperature 293.15 K). The experimental data were analyzed using sorption kinetic models (pseudo-first- and pseudo-second-order equations) to determine the equation that fits best our experimental results. Equilibrium isotherm studies were used to evaluate the maximum sorption capacity of activated carbon and experimental results showed this to be 28.30 mg/g. The Freundlich, Langmuir, and Dubinin-Radushkevich (D-R) models have been applied and the data correlate well with Freundlich model and that the sorption is physical in nature (the activation energy Ea=7.91 kJ/mol). Thermodynamic parameters (DeltaHads0=-50.53 kJ/mol, DeltaSads0=-98.76 J/mol K, DeltaGads(293.15 K)0=-21.61 kJ/mol) showed the exothermic heat of adsorption and the feasibility of the process.     

Effective adsorption of U(VI) from aqueous solution using magnetic chitosan nanoparticles grafted with maleic anhydride: equilibrium,kinetic and thermodynamic studies

The in situ formed magnetite nanoparticles was encapsulated by maleated chitosan to synthesize a novel magnetic chitosan nano-sorbent (MCN-MA) for the effective sorption of uranium. The sorption kinetics could be described by the pseudo-second-order model, whereas the sorption isotherms could be fitted to the Langmuir model (q _m = 187.9 mg/g). The MCN-MA showed higher U(VI) sorption capacities (compared to MCN) due to high affinity of carboxylate groups introduced from grafting maleic anhydride. Thermodynamic parameters indicate that U(VI) sorption is endothermic and feasible. The nano-size and magnetic property of the MCN-MA allow its efficient U(VI) sorption and facile magnetic separation from wastewaters.     

Uranium (VI) adsorption on synthesized 4A and P1 zeolites: Equilibrium,kinetic, and thermodynamic studies

The present work deals with the investigation of the use of synthesized 4A and P1 zeolites in the adsorption of uranium (VI) ions from liquid effluents (with initial concentrations of 100, 85 and 80 mg·L⁻¹). Batch experiments were performed and the effects of temperature, solid–liquid ratio, pH and initial UO₂²⁺ ion concentration were studied, and the optimal parameters were determined. The kinetic and thermodynamic aspects of the process as well as the diffusion mechanism have been studied. The obtained results showed that 4A and P1 zeolites are very effective adsorbents.     

Adsorption kinetic, isotherm and thermodynamic studies of Sr2+ onto hexagonal tungsten oxide

Hexagonal tungsten oxide (hex-WO₃) with exchangeable sodium and ammonium cations located in hexagonal channel was synthesized by a facile hydrothermal treatment of sodium tungstate dihydrate in concentrated HCl solution in the presence of ammonium sulfate. An attempt was made to assess the potential of hex-WO₃ for the adsorption of Sr²⁺ ions from acidic radioactive waste solutions. Adsorption of Sr²⁺ reached equilibrium very quickly in 2 h in acidic aqueous solution. Maximum removal of Sr²⁺ ions occurred at pH 4. Equilibrium studies showed that the extent of Sr²⁺ ions uptake by hex-WO₃ was better described by the Freundlich isotherm in comparison with the Langmuir model. The thermodynamic parameters showed that the adsorption of Sr²⁺ ions onto hex-WO₃ was spontaneous and exothermic under the studied conditions.     

Uranium(VI) recovery from its leach liquor using zirconium molybdophosphate composite: kinetic,equilibrium and thermodynamic studies

Journal of Radioanalytical and Nuclear Chemistry - A zirconium molybdophosphate composite was designed for the selective recovery of uranium ions. The synthesized composite was well-characterized...     

Biosorption characteristics of uranium(VI) from aqueous solution by pummelo peel

The biomass pummelo peel was chosen as a biosorbent for removal of uranium(VI) from aqueous solution. The feasibility of adsorption of U(VI) by Pummelo peel was studied with batch adsorption experiments. The effects of contact time, biosorbent dosage and pH on adsorption capacity were investigated in detail. The pummelo peel exhibited the highest U(VI) sorption capacity 270.71?mg/g at an initial pH of 5.5, concentration of 50???g/mL, temperature 303?K and contacting time 7?h. The adsorption process of U(VI) was found to follow the pseudo-second-order kinetic equation. The adsorption isotherm study indicated that it followed both the Langmuir adsorption isotherm and the Freundlich adsorption isotherm. The thermodynamic parameters values calculated clearly indicated that the adsorption process was feasible, spontaneous and endothermic in nature. These properties show that the pummelo peel has potential application in the removal of the uranium(VI) from the radioactive waste water.